1. Field of the Invention
The present invention relates to a rich-lean (off-stoichiometric) burner (a low NOx burner) that includes an inner tube to which lean gas is supplied, and an outer tube which is coaxially disposed around the inner tube and to which rich gas is supplied. The rich-lean burner is used in a gas combustion device, such as a warm air heater.
2. Description of Related Art
In a gas combustion device, such as a warm air heater, a rich-lean burner (a low NOx burner) is used in some cases in order to reduce a discharge amount of NOx (nitrogen oxides). The rich-lean burner forms a main flame by causing an air-fuel mixture (lean gas) in which the fuel is leaner than a stoichiometric air-fuel ratio to combust in a lean flame hole, and forms a pilot flame by causing an air-fuel mixture (rich gas) in which the fuel is richer than the stoichiometric air-fuel ratio to combust in a rich flame hole that is adjacent to the lean flame hole.
For example, Japanese Patent Application Publication No. JP 6-147426A discloses a rich-lean burner which includes a double tube having an inner tube and an outer tube, and in which an end portion of the inner tube is used as a lean flame hole and a space between the inner tube and the outer tube is used as a rich flame hole. In the rich-lean burner, an entire end face of the double tube is covered by wire netting in order to achieve stable ignition and improve mixture of lean gas.